Metal fiber sintered body for surface combustion

ABSTRACT

Disclosed herein is a metal fiber sintered body for combustion used for combustion media of gas burners. The sintered body comprises a plurality of circular though-holes, each having a diameter of 0.5˜2 mm, formed in a regular pattern therein. The sintered body has a metal fiber density in the range of 0.5˜4 kg/m 2 , and a total area of the through-holes is less than 5% of a total surface area of the metal fiber sintered body. The metal fibers may comprise Fe—Cr—Al-based alloys, and further comprise trace elements. When the sintered body is applied to the combustion media, the fuel gas is prevented from being concentrated on the center of the through holes and leaked therethrough, while the length of combustion flames is reduced, thereby enabling complete combustion as well as allowing the combustion chamber to be manufactured at a reduced scale.

RELATED APPLICATION

The present invention is based on, and claims priority from, Korean Application Number 2004-41846, filed on Jun. 8, 2004, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a metal fiber sintered body for combustion used for combustion media of gas combustors including burners, gas ranges, gas boilers or the like, and, more particularly, to a metal fiber sintered body for surface combustion, which enables high-load surface combustion.

2. Description of the Related Art

Combustors comprise combustion media, for example, plate-shaped porous combustion media, for burning a supplied fuel.

One example of a porous plate for combustion media of a combustor is disclosed in Korean Patent Laid-open publication No. 1995-7000517 (WO 93/018342) entitled “Porous metal fiber plate, and gas burner using the same.”

The porous metal fiber plate of the disclosure comprises through holes or passages regularly formed in the plate such that the total area of free passages (through holes) is 5 to 35% of the total surface area of the plate, and each of the holes has a surface area of 0.03 to 10 m².

However, when the total area of free passages (through holes) is 5% or more of the total surface area of the plate as described above, gas or air tends to concentrate on the through holes, thereby lowering a pressure difference over the media, and when a discharge amount of the gas or air is increased for high-load combustion, a fuel gas is deviated from a burning region before being burnt, thereby interfering with manufacturing of combustion media of high heat capacity.

Another example of the porous plate for combustion media of the combustor is a metal fiber film for a gas burner disclosed in Korean Patent Laid-open publication No. 1996-7002898 (WO 95/027871).

The metal fiber film for the gas burner of the disclosure comprises a rectangular lattice-shaped porous zone, and an intermediate sealing zone.

The metal fiber film for the gas burner is burnt by means of metal fibers heated on the surface of the combustion media supplied through the porous zones. Accordingly, although the metal fiber film of the disclosure is appropriate for low-load combustion, it is inappropriate for high-load combustion.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a metal fiber sintered body for surface combustion, which enables combustion of the entire surface of the sintered body.

In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a metal fiber sintered body for combustion media of gas burners, comprising: a plurality of circular though-holes formed in a regular pattern in the metal fiber sintered body, wherein the metal fiber sintered body has a metal fiber density in the range of 0.5˜4 kg/m², each of the through-holes has a diameter of 0.5˜2 mm, and the total area of the through-holes is less than 5% of the total surface area of the metal fiber sintered body.

In accordance with another aspect of the present invention, a metal fiber sintered body for combustion media of gas burners, wherein the sintered body has a metal fiber density in the range of 0.5˜4 kg/m².

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and features of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a micrograph illustrating one example of a surface of a metal fiber sintered body for surface combustion according to the present invention;

FIG. 2 is a schematic view illustrating a flame shape of a conventional gas burner;

FIG. 3 is a schematic view illustrating a flame shape of combustion media for a conventional gas touch;

FIG. 4 is a schematic view illustrating a flame shape of a metal fiber sintered body for surface combustion according to the present invention;

FIG. 5 is a graphical representation illustrating variation in increase of an oxidized weight for metal fibers without an added trace element, and for metal fibers having Ti, Nb or Zr added as trace elements thereto; and

FIG. 6 is a graphical representation illustrating a heating time taken to heat the same amount of water to 100° C. with the same amount of gas by use of burners made of an inventive material, a comparative material, and a conventional material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments will now be described in detail with reference to the accompanying drawings.

A metal fiber sintered body for surface combustion according to the invention is applied to combustion media of combustors, and is preferably applied to combustion media of high-load burners.

The sintered body of the invention may be manufactured by randomly arranging and sintering metal fibers.

The metal fibers preferably include metal fibers of rapidly solidified Fe—Cr—Al-based alloys, and more preferably metal fibers of rapidly solidified Fe—Cr—Al-trace element-based alloys.

The Fe—Cr—Al-based alloy preferably comprises: 70˜83 wt % of Fe; 18˜27 wt % of Cr; and 3˜7 wt % of Al.

The content of trace element is preferably in the range of 0.05˜0.5 wt %.

The trace element is preferably one of Zr, Nb, and Ti, and most preferably Zr.

It should be noted that the method for manufacturing the metal fibers is not limited to the method described above.

As disclosed in Korean Patent No. 178643 and U.S. Pat. No. 6,604,670, preferable examples of a method for manufacturing the metal fibers include a rapid solidification method in which a portion of a metal bar is melted, and is then rapidly solidified by bring it into contact with a cooling disk rotating at a high speed in order to produce the metal fibers.

With the rapid solidification method, the metal fibers are produced to a particle size of about 5˜20 μm.

The metal fibers having a fine particle size of about 5˜20 μm as described above can be more appropriately used for the combustion media of gas burners. This is attributed to the fact that the oxidation resistance of the metal fibers is increased with decreasing particle size, and high oxidation resistance is required of combustion media.

The metal fibers can be produced by typical drawing or cutting, and in this case, the metal fibers have a particle size of 50 μm or more. As a result, the metal fibers produced by drawing or cutting have an oxidation-induced weight increase two times that of the metal fibers produced by the rapid solidification method. Thus, life span of the metal fibers produced by drawing or cutting is shorter than that of the metal fibers produced by the rapid solidification method.

In FIG. 1, one example of the metal fiber sintered body for surface combustion is illustrated, in which through holes are formed through the sintered body.

Unlike the combustion with flames created at a portion of a burning part, as shown in FIGS. 2 and 3, when applying the metal fiber sintered body of the invention to the combustion media, flames having a short length are created over the entire surface of a burning part, as shown in FIG. 4, thereby enhancing thermal efficiency and stability while reducing generation of toxic gases.

When the diameter of the through-holes formed in the metal fiber sintered body of the invention is significantly reduced, there is a possibility that a fuel gas for combustion is not appropriately discharged therethrough depending on the operating conditions of the sintered body, causing backfires wherein flames are created from the lower end of the combustion media. On the other hand, when the diameter of through-holes is significantly increased, the fuel gas is concentrated on the through-holes, so that combustion occurs only in the through holes rather than over the entire surface of the combustion media. Accordingly, the through holes preferably have a diameter of 0.5˜2 mm.

When the total area of the through-holes is significantly large compared with the total surface area of the metal fiber sintered body, the fuel gas is concentrated on the center of the holes, so that a small amount of fuel gas is leaked, and the length of the flames is increased, thereby causing a combustion chamber of the burner to be enlarged. Thus, the total area of the through-holes is preferably less than 5% of the total surface area of the sintered body.

According to the invention, it is desirable that the through-holes be formed in a regular pattern in the sintered body for the purpose of providing a more uniform shape of surface combustion.

If the through-holes are formed in an irregular pattern in the sintered body, the fuel gas can be non-uniformly distributed, thereby increasing the intensity of combustion, which in turn can result in concentration of the fuel gas on a portion having a higher intensity of combustion, thereby causing fracture of the combustion media.

As for the regular pattern of the through holes, it preferably has a triangular shape or a rectangular shape. This is attributed to the fact that the triangular or rectangular shape is advantageous in that it provides a uniform arrangement of the through holes, thereby enabling uniform surface combustion.

According to the present invention, the sintered body need not necessarily have the through holes formed therethrough.

The sintered body of the invention preferably has a porosity of 70˜95%. If the sintered body has a significantly lower porosity, the fuel gas and air cannot be discharged through the fine pores, whereby surface combustion cannot be achieved. If the sintered body has a significantly higher porosity, the temperature of the burning surface is similar to that of the portion where the gas is supplied, causing backfires.

According to the invention, the metal fibers constituting the sintered body have a density of 0.5˜4 kg/m². If the metal fibers have a significantly lower density, the number of metal fibers constituting the sintered body is significantly reduced, causing the supplied fuel gas to be emitted through the pores before being burnt, so that the sintered body cannot be applied to the combustion media. If the metal fibers have a significantly higher density, the thickness of the sintered body is significantly increased, making it difficult to form the through holes therein, and causing fine flames provided as an advantage of the surface combustion media not to be formed through the through holes.

The metal fibers preferably have a diameter of 20˜80 μm. If the metal fibers have a significantly smaller diameter, it is difficult to form the fine pores appropriate for the surface combustion in the sintered body, and if the metal fibers have a significantly larger diameter, the size of the pores is significantly increased, so that the sintered body having such large pores cannot be applied to combustion media having a lower density.

That is, when the metal fibers have the diameter and the density as described above according to the invention, the fine pores are uniformly formed in the sintered body, thereby enabling more sufficient surface combustion.

Preferably, when the through holes are formed in the triangular pattern, spacing between the through holes is 1˜5 mm, and when the through holes are formed in the rectangular pattern, spacing between the through holes is 1˜6 mm. If the space between the through holes is significantly narrow, the density of through holes present on the surface of the sintered body is significantly increased, thereby increasing consumption of fuel gas and lowering thermal efficiency. If the space between the through holes is significantly wide, the density of through holes present on the surface of the sintered body is significantly lowered, whereby a proper level of flames is not formed depending on the operating conditions of the sintered body and thus thermal efficiency is lowered.

The metal fiber sintered body of the invention as described above may be manufactured by randomly arranging appropriately produced metal fibers, and sintering the same under appropriate vacuum conditions.

Preferred vacuum sintering occurs at a vacuum of 10⁻⁵10⁻⁶ Torr, a sintering temperature of 1,200˜1,400° C., and a sintering time of 1˜4 hours.

The present invention will be described in detail with reference to examples as follows.

EXAMPLE 1

After producing metal fibers having composition, diameter, density, and particle size as shown in the following Table 1 according to the rapid solidification method disclosed in Korean Patent No. 178643, the metal fibers were oxidized at 1,000° C., and an increase of oxidized weight was measured. Results of the measurement are shown in FIG. 5. TABLE 1 Composition (wt %) Particle Trace Diameter Density size No. Fe Cr Al element (μm) (kg/m²) (μm) Metal fiber Balance 18˜22 4˜6 — 40 1˜4 10 without trace elements Zr-added Balance 18˜22 4˜6 Zr: 0.3 40 1˜4 10 metal fiber Nb-added Balance 18˜22 4˜6 Nb: 0.3 40 1˜4 10 metal fiber Ti-added Balance 18˜22 4˜6 Ti: 0.3 40 1˜4 10 metal fiber

As shown in FIG. 5, it can be appreciated that when the trace element is added to the metal fibers according to the invention, the increase of oxidized weight is lower than the metal fibers without the trace element, and in particular when Zr is added as the trace element to the metal fibers, the increment of oxidized weight is the lowest.

In other words, it can be appreciated that the metal fibers having the trace element added thereto exhibit excellent oxidation resistance, and in particular when Zr is added to the metal fibers, the increment of oxidized weight is about 6%, thereby providing excellent oxidation resistance.

EXAMPLE 2

Sintered bodies having the shapes shown in Table 2 were produced by randomly arranging the Zr-added metal fibers of Table 1, and sintering the same under vacuum. Then, intensity of combustion was measured for the sintered bodies. Results of the measurement are shown in the following Table 3. TABLE 2 Through holes Diameter Ratio to a total Sintered body No. (mm) Shape surface area Arrangement Inventive 0.8 Circular 4.74% Triangular sintered body pattern Comparative 0.8 Circular   6% Triangular sintered body 1 pattern Comparative 1.0 Circular 14.5% Triangular sintered body 2 pattern

TABLE 3 Sintered body No. Intensity of combustion (kW/m²) Inventive sintered body 5.342 Comparative sintered body 1 5.293 Comparative sintered body 2 5.176

As shown in Table 3, it can be appreciated that the Inventive sintered body of the invention exhibits an excellent intensity of combustion compared to those of Comparative sintered bodies 1 and 2.

EXAMPLE 3

An inventive burner and a comparative burner were manufactured using the inventive sintered body and the comparative sintered body 2 of Example 2 shown in Table 3 for combustion media, respectively.

With the inventive burner, the comparative burner, and the conventional burner having combustion properties of a gas range shown in FIG. 2, a heating time taken to heating the same amount of water to 100° C. with the same amount of gas was measured, and results thereof are shown in FIG. 6.

As shown in FIG. 6, it can be appreciated that the inventive burner using the inventive sintered body heats water to 100° C. about 20 seconds faster than the comparative burner using the comparative sintered body, and about 100 seconds faster than the conventional burner.

Accordingly, it can be appreciated that the metal fiber sintered body can be used for the burner enabling high-load combustion and providing excellent combustion efficiency.

As apparent from the description, the present invention provides a metal fiber sintered body for surface combustion, which is designed to enable combustion over the entire surface thereof, so that, when this sintered body is applied to the combustion media of the burner, the fuel gas is prevented from being concentrated on the center of the through holes and leaked through the through holes. Furthermore, the length of combustion flames is reduced, and thus complete combustion can be achieved, thereby solving the problem of discharge gas caused by incomplete combustion as well as allowing the combustion chamber to be manufactured at a reduced scale.

It should be understood that the embodiments and the accompanying drawings have been described for illustrative purposes and the present invention is limited only by the following claims. Further, those skilled in the art will appreciate that various modifications, additions and substitutions are allowed without departing from the scope and spirit of the invention as set forth in the accompanying claims. 

1. A metal fiber sintered body for combustion media of combustors, comprising: a plurality of circular though-holes formed in a regular pattern in the metal fiber sintered body, wherein the metal fiber sintered body has a metal fiber density in the range of 0.5˜4 kg/m², each of the through-holes has a diameter of 0.5˜2 mm, and a total area of the through-holes is less than 5% of a total surface area of the metal fiber sintered body.
 2. The sintered body as set forth in claim 1, wherein a space between the through holes is 1˜5 mm, and the through holes are regularly arranged in a triangular pattern.
 3. The sintered body as set forth in claim 1, wherein a space between the through holes is 1˜6 mm, and the through holes are regularly arranged in a rectangular pattern.
 4. The sintered body as set forth in any one of claims 1 to 3, wherein the metal fibers have a diameter of 20˜80 μm.
 5. The sintered body as set forth in any one of claims 1 to 3, wherein the metal fibers comprise Fe—Cr—Al-based alloys.
 6. The sintered body as set forth in claim 4, wherein the metal fibers comprise Fe—Cr—Al-based alloys.
 7. The sintered body as set forth in claim 5, wherein the metal fibers further comprise 0.05˜0.5 wt % of Zr.
 8. The sintered body as set forth in claim 6, wherein the metal fibers further comprise 0.05˜0.5 wt % of Zr.
 9. The sintered body as set forth in any one of claims 1 to 3, wherein the sintered body has a porosity of 70˜95%.
 10. A metal fiber sintered body for combustion media of combustors, wherein the sintered body has a metal fiber density in the range of 0.5˜4 kg/m². 